There exists a need for a blood-substitute to treat or prevent hypoxia resulting from blood loss (e.g, from acute hemorrhage or during surgical operations), resulting from anemia (e.g., pernicious anemia or sickle cell anemia), or resulting from shock (e.g, volume deficiency shock, anaphylactic shock, septic shock or allergic shock).
The use of blood and blood fractions as in these capacities as a blood-substitute is fraught with disadvantages. For example, the use of whole blood often is accompanied by the risk of transmission of hepatitis-producing viruses and AIDS-producing viruses which can complicate patient recovery or result in patient fatalities. Additionally, the use of whole blood requires blood-typing and cross-matching to avoid immunohematological problems and interdonor incompatibility.
Human hemoglobin, as a blood-substitute, possesses osmotic activity and the ability to transport and transfer oxygen, but it has the disadvantage of rapid elimination from circulation by the renal route and through vascular walls, resulting in a very short, and therefore, a typically unsatisfactory half-life. Further, human hemoglobin is also frequently contaminated with toxic levels of endotoxins, bacteria and/or viruses.
Non-human hemoglobin suffers from the same deficiencies as human hemoglobin. In addition, hemoglobin from non-human sources is also typically contaminated with proteins, such as antibodies, which could cause an immune system response in the recipient.
Previously, at least four other types of blood-substitutes have been utilized, including perfluorochemicals, synthesized hemoglobin analogues, liposome-encapsulated hemoglobin, and chemically-modified hemoglobin. However, many of these blood-substitutes have typically had short intravascular retention times, being removed by the circulatory system as foreign substances or lodging in the liver, spleen, and other tissues. Also, many of these blood-substitutes have been biologically incompatible with living systems.
Thus, in spite of the recent advances in the preparation of hemoglobin-based blood-substitutes, the need has continued to exist for a blood-substitute which has levels of contaminants, such as endotoxins, bacteria, viruses, phospholipids and non-hemoglobin proteins, which are sufficiently low to generally prevent an immune system response and any toxicological effects resulting from an infusion of the blood-substitute. In addition, the blood-substitute must also be capable of transporting and transferring adequate amounts of oxygen to tissue under ambient conditions and must have a good intravascular retention time.
Further, it is preferred that the blood-substitute 1) has an oncotic activity generally equivalent to that of whole blood, 2) can be transfused to most recipients without cross-matching or sensitivity testing, and 3) can be stored with minimum amounts of refrigeration for long periods.